With the ever increasing awareness of pollution problems in contemporary society, and with the ever increasing volume of waste products which forms a natural byproduct of growth in the industrialized world, there have been ever increasing demands placed upon the requirements of new sewage treatment plants, and also demands for improvement of existing systems. In my patents U.S. Pat. Nos. 3,743,100, dated July 3, 1973, entitled FILTER PRESS, MORE PARTICULARLY FOR DEWATERING SLUDGE IN SEWAGE TREATMENT PLANTS, and 3,896,030, dated July 32, 1975, entitled identically to the first mentioned patent, I have described certain filter press systems to be advantageously used for the facilitation of sludge. In the latter patent, 030, I have also discussed a dewatering system which has been based on the principle of simply straining sludge through the action of gravity. It was pointed out in the 030 patent that various known filter presses possess a preliminary dewatering section, which is essentially a straining system, while in other cases the material on the filter belt is first squeezed between pressure rollers, prior to treatment on a rotary drum system. The filter press dewatering means described in this prior art in the 030 patent have the disadvantage that filtering efficiency is comparatively low, the contruction relatively complex, and the space occupied by the machine is relatively great. In my 030 patent there is described a new dewatering means which has a pretreatment system, whereby the sludge, prior to reaching the rotary belt is pressed between two filter belts, with a filter belt acting as a strainer. Thus, through the action of gravity an appreciable amount of the water is removed, thus reducing the total water content of the sludge prior to entering the rotary drum system. In my copending patent application, Bahr, U.S. Ser. No. 632,789, entitled SLUDGE PRETREATMENT DEWATERING BASED UPON A CONTINUOUS SYSTEM OF FILTER POCKETS, filed on even date herewith, there is described an advantageous method for partially dewatering sludge prior to treatment of the sludge in a conventional filter press. This system in part serves to improve existing sludge treatment systems, and this system of said copending patent application may be incorporated into the method and apparatus of a second copending patent application, Bahr, U.S. Ser. No. 632,689 entitled CONSECUTIVE, INDEPENDENT DEWATERING APPARATUS AND METHOD FOR IMPROVED SLUDGE TREATMENT, filed on even date herewith.